The pancreas from normal human fetuses between 16-20 weeks gestational age will be isolated, dispersed, and cultured under conditions previously demonstrated suitable for long-term maintenance of guinea pig islets at this institution. These conditions will be modified to support maintenance of viable human fetal islets for up to 60 days. During this period, cultures will be evaluated for islet cell maturation with loss of acinar tissue, morphological changes as assessed by light and electron microscopy, and physiological maturation of basal and stimulated insulin secretion. In addition, intact fetal pancreases and fetal pancreatic tissue both before and after culture, will be stored at -187 degrees C. The effect of this procedure on the above variables and the effect of subsequent culture on repair of freeze injury will be assessed. Simultaneously, membrane insulin receptors of fresh, cultured, and cryopreserved fetal islet cells will be defined and characterized. Moreover, insulin receptor concentration will be correlated with glucose and amino acid transport. It is anticipated that data from these investigations will provide further insight into the mechanisms of insulin secretion, and provide the basis for the establishment of an islet cell "bank" to serve as a source of material for investigators in other biomedical fields and as a source of donor tissue for future islet transplantation in diabetic man.